O-GlcNAcylation promotes fatty acid synthase activity under nutritional stress as a pro-survival mechanism in cancer cells

Implications and mechanisms of O-GlcNAcylation in cancer therapy resistance

O-linked-N-acetylglucosaminylation (O-GlcNAcylation), one of the protein post-translational modifications, is the process of adding O-linked-β-D-N-acetylglucosaminylation (O-GlcNAc) to serine and threonine residues of proteins. O-GlcNAcylation regulates various fundamental cell biological processes, including gene transcription, signal transduction, and cellular metabolism. The role of dysregulated O-GlcNAcylation in tumorigenesis has been recognized, but its role in cancer therapy tolerance has not been elucidated. Therefore, this paper provides the latest evidence on the role of O-GlcNAcylation in cancer therapy responsiveness to understand the impact of O-GlcNAcylation on cancer therapy outcomes, as well as analyzing several possible mechanisms by which O-GlcNAcylation dysregulation affects cancer therapy efficacy, and discusses the possibility of O-GlcNAcylation as a cancer therapy sensitizer.

Delactylation diminished the growth inhibitory role of CA3 by restoring DUOX2 expression in hepatocellular carcinoma

Lactylation is an emerging pathogenesis of hepatocellular carcinoma (HCC). However, the underlying mechanisms and biological significance remain poorly understood. The Carbonic anhydrase III (CA3) gene, previously defined as a binding protein of SQLE and involved in the NAFLD disease, has now been identified as a novel tumor suppressor in HCC. mRNA expression of CA3 is associated with a favorable prognosis and negatively correlated with serum lactate levels, whereas CA3 protein expression does not correlate with patient prognosis or serum lactate levels, suggested there has lactate-related post-translational modification of CA3 in HCC. Overexpression of CA3 induces cell apoptosis, thereby reducing intracellular reactive oxygen stress (ROS) through the inhibition of DUOX2 expression. The decreased lactylation level of CA3 protein at the K36 residues, induced by SQLE, results in the loss of the anti-cancer effect of CA3. Together, this study has demonstrated that CA3 is a novel tumor suppressor in HCC, and delactylation of CA3 represents a newly identified mechanism by which HCC cells evade growth suppressors.

Mapping O- and N-Glycosylation in Transmembrane and Interface Regions of Proteins: Insights from a Database Search Study

Glycosylation is a critical post-translational modification that influences protein folding, stability and function. While extensively studied in extracellular and intracellular regions, glycosylation within transmembrane (TM) regions and at membrane interfaces remains poorly understood. This study aimed to map O- and N-glycosylation sites in these regions using a comprehensive database search and structural validation where possible. Extensive database searches revealed glycosylation sites in a range of membrane proteins. Only the sites falling in the TM regions and at the membrane interface (according to Uniprot annotations) were retained. The location of these sites was confirmed based on available 3D structures. We identified 32 O-glycosylation sites and 7 N-glycosylation sites in the TM domains of 29 proteins. O-GlcNAc sites validated as located within TM regions presented side chains either oriented toward the lipid bilayer or buried within the protein. N-glycosylation sites predicted in protein TM regions were largely confined to interface or extracellular domains. The results obtained here highlight the occurrence of glycosylation in TM regions of proteins and at membrane interfaces. This dataset provides a valuable foundation for the further exploration of structural and functional roles of glycosylation in membrane-associated regions.

Opportunities for Therapeutic Modulation of O-GlcNAc

O-Linked β-N-acetylglucosamine (O-GlcNAc) is an essential, dynamic monosaccharide post-translational modification (PTM) found on serine and threonine residues of thousands of nucleocytoplasmic proteins. The installation and removal of O-GlcNAc is controlled by a single pair of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery four decades ago, O-GlcNAc has been found on diverse classes of proteins, playing important functional roles in many cellular processes. Dysregulation of O-GlcNAc homeostasis has been implicated in the pathogenesis of disease, including neurodegeneration, X-linked intellectual disability (XLID), cancer, diabetes, and immunological disorders. These foundational studies of O-GlcNAc in disease biology have motivated efforts to target O-GlcNAc therapeutically, with multiple clinical candidates under evaluation. In this review, we describe the characterization and biochemistry of OGT and OGA, cellular O-GlcNAc regulation, development of OGT and OGA inhibitors, O-GlcNAc in pathophysiology, clinical progress of O-GlcNAc modulators, and emerging opportunities for targeting O-GlcNAc. This comprehensive resource should motivate further study into O-GlcNAc function and inspire strategies for therapeutic modulation of O-GlcNAc.

O-GlcNAcylation in tumorigenesis and its implications for cancer therapy

O-linked N-acetylglucosaminylation (O-GlcNAcylation) is a dynamic and reversible posttranslational modification that targets serine and threonine residues in a variety of proteins. Uridine diphospho-N-acetylglucosamine, which is synthesized from glucose via the hexosamine biosynthesis pathway, is the major donor of this modification. O-GlcNAc transferase is the sole enzyme that transfers GlcNAc onto protein substrates, while O-GlcNAcase is responsible for removing this modification. O-GlcNAcylation plays an important role in tumorigenesis and progression through the modification of specific protein substrates. In this review, we discuss the tumor-related biological functions of O-GlcNAcylation and summarize the recent progress in the development of pharmaceutical options to manipulate the O-GlcNAcylation of specific proteins as potential anticancer therapies.

Fatty acid synthase (FASN) signalome: A molecular guide for precision oncology

The initial excitement generated more than two decades ago by the discovery of drugs targeting fatty acid synthase (FASN)-catalyzed de novo lipogenesis for cancer therapy was short-lived. However, the advent of the first clinical-grade FASN inhibitor (TVB-2640; denifanstat), which is currently being studied in various phase II trials, and the exciting advances in understanding the FASN signalome are fueling a renewed interest in FASN-targeted strategies for the treatment and prevention of cancer. Here, we provide a detailed overview of how FASN can drive phenotypic plasticity and cell fate decisions, mitochondrial regulation of cell death, immune escape and organ-specific metastatic potential. We then present a variety of FASN-targeted therapeutic approaches that address the major challenges facing FASN therapy. These include limitations of current FASN inhibitors and the lack of precision tools to maximize the therapeutic potential of FASN inhibitors in the clinic. Rethinking the role of FASN as a signal transducer in cancer pathogenesis may provide molecularly driven strategies to optimize FASN as a long-awaited target for cancer therapeutics.

Protein O-GlcNAcylation: The sweet hub in liver metabolic flexibility from a (patho)physiological perspective

O-GlcNAcylation is a dynamic, reversible and atypical O-glycosylation that regulates various cellular physiological processes via conformation, stabilisation, localisation, chaperone interaction or activity of target proteins. The O-GlcNAcylation cycle is precisely controlled by collaboration between O-GlcNAc transferase and O-GlcNAcase. Uridine-diphosphate-N-acetylglucosamine, the sole donor of O-GlcNAcylation produced by the hexosamine biosynthesis pathway, is controlled by the input of glucose, glutamine, acetyl coenzyme A and uridine triphosphate, making it a sensor of the fluctuation of molecules, making O-GlcNAcylation a pivotal nutrient sensor for the metabolism of carbohydrates, amino acids, lipids and nucleotides. O-GlcNAcylation, particularly prevalent in liver, is the core hub for controlling systemic glucose homeostasis due to its nutritional sensitivity and precise spatiotemporal regulation of insulin signal transduction. The pathology of various liver diseases has highlighted hepatic metabolic disorder and dysfunction, and abnormal O-GlcNAcylation also plays a specific pathological role in these processes. Therefore, this review describes the unique features of O-GlcNAcylation and its dynamic homeostasis maintenance. Additionally, it explains the underlying nutritional sensitivity of O-GlcNAcylation and discusses its mechanism of spatiotemporal modulation of insulin signal transduction and liver metabolic homeostasis during the fasting and feeding cycle. This review emphasises the pathophysiological implications of O-GlcNAcylation in nonalcoholic fatty liver disease, nonalcoholic steatohepatitis and hepatic fibrosis, and focuses on the adverse effects of hyper O-GlcNAcylation on liver cancer progression and metabolic reprogramming.

Role of O-GlcNAcylation in cancer biology

One of the general characteristics of cancer cells is the abnormal increase of O-GlcNAcylation. Recent studies have shown that it affects the basic functions of proteins and regulates multiple phenotypes of cancer cells through key signals and metabolic pathways. O-GlcNAcylation is a covalent linkage between the β-D-N-acetylglucosamine (GlcNAc) sugar and target protein. It interacts with many other types of post-translational modifications and works together in the whole process of cancer development. For example, it regulates cell activities such as cell signal transduction, transcription, cell division, metabolism and cytoskeleton regulation. In this review, we summarized the general concept of O-GlcNAcylation and its related role in the ten major tumor phenotypes.

O-GlcNAcylation and Its Roles in Neurodegenerative Diseases

 As a non-classical post-translational modification, O-linked β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) is widely found in human organ systems, particularly in our brains, and is indispensable for healthy cell biology. With the increasing age of the global population, the incidence of neurodegenerative diseases is increasing, too. The common characteristic of these disorders is the aggregation of abnormal proteins in the brain. Current research has found that O-GlcNAcylation dysregulation is involved in misfolding or aggregation of these abnormal proteins to mediate disease progression, but the specific mechanism has not been defined. This paper reviews recent studies on O-GlcNAcylation's roles in several neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, Machado-Joseph's disease, and giant axonal neuropathy, and shows that O-GlcNAcylation, as glucose metabolism sensor, mediating synaptic function, participating in oxidative stress response and signaling pathway conduction, directly or indirectly regulates characteristic pathological protein toxicity and affects disease progression. The existing results suggest that targeting O-GlcNAcylation will provide new ideas for clinical diagnosis, prevention, and treatment of neurodegenerative diseases.

O-GlcNAcylation at the center of antitumor immunity

The post-translational modification known as O-GlcNAcylation is a highly dysregulated process in tumors, and a key contributor to malignant transformation. In contrast, after three decades since its discovery, very little has been revealed about this process in the immune system. With the prospect of targeting O-GlcNAcylation as tumor therapy, greater understanding of how it regulates immune responses in the context of the tumor microenvironment will be needed. Here, we discuss recent discoveries from which a picture is emerging that O-GlcNAcylation, in either tumors or in immune cells, could negatively impact overall antitumor immune responses. We propose that interference with O-GlcNAcylation thus holds promise for cancer treatment from both perspectives.

On a sugar high: Role of O-GlcNAcylation in cancer

Recent advances in the understanding of the molecular mechanisms underlying cancer progression have led to the development of novel therapeutic targeting strategies. Aberrant glycosylation patterns and their implication in cancer have gained increasing attention as potential targets due to the critical role of glycosylation in regulating tumor-specific pathways that contribute to cancer cell survival, proliferation, and progression. A special type of glycosylation that has been gaining momentum in cancer research is the modification of nuclear, cytoplasmic, and mitochondrial proteins, termed O-GlcNAcylation. This protein modification is catalyzed by an enzyme called O-GlcNAc transferase (OGT), which uses the final product of the Hexosamine Biosynthetic Pathway (HBP) to connect altered nutrient availability to changes in cellular signaling that contribute to multiple aspects of tumor progression. Both O-GlcNAc and its enzyme OGT are highly elevated in cancer and fulfill the crucial role in regulating many hallmarks of cancer. In this review, we present and discuss the latest findings elucidating the involvement of OGT and O-GlcNAc in cancer.

Excessive gluconeogenesis causes the hepatic insulin resistance paradox and its sequelae

Background

Hepatic insulin signaling suppresses gluconeogenesis but promotes de novo lipid synthesis. Paradoxically, hepatic insulin resistance (HIR) enhances both gluconeogenesis and de novo lipid synthesis. Elucidation of the etiology of this paradox, which participates in the pathogenesis of non-alcoholic fatty liver disease (NAFLD), cardiovascular disease, the metabolic syndrome and hepatocellular carcinoma, has not been fully achieved.

Scope of review

This article briefly outlines the previously proposed hypotheses on the etiology of the HIR paradox. It then discusses literature consistent with an alternative hypothesis that excessive gluconeogenesis, the direct effect of HIR, is responsible for the aberrant lipogenesis. The mechanisms involved therein are explained, involving de novo synthesis of fructose and uric acid, promotion of glutamine anaplerosis, and induction of glucagon resistance. Thus, gluconeogenesis via lipogenesis promotes hepatic steatosis, a component of NAFLD, and dyslipidemia. Gluconeogenesis-centred mechanisms for the progression of NAFLD from simple steatosis to non-alcoholic steatohepatitis (NASH) and fibrosis are suggested. That NAFLD often precedes and predicts type 2 diabetes is explained by the ability of lipogenesis to cushion against blood glucose dysregulation in the earlier stages of NAFLD.

Major conclusions

HIR-induced excessive gluconeogenesis is a major cause of the HIR paradox and its sequelae. Such involvement of gluconeogenesis in lipid synthesis rationalizes the fact that several types of antidiabetic drugs ameliorate NAFLD. Thus, dietary, lifestyle and pharmacological targeting of HIR and hepatic gluconeogenesis may be a most viable approach for the prevention and management of the HIR-associated network of diseases.

Protein O-GlcNAcylation in Metabolic Modulation of Skeletal Muscle: A Bright but Long Way to Go

O-GlcNAcylation is an atypical, dynamic and reversible O-glycosylation that is critical and abundant in metazoan. O-GlcNAcylation coordinates and receives various signaling inputs such as nutrients and stresses, thus spatiotemporally regulating the activity, stability, localization and interaction of target proteins to participate in cellular physiological functions. Our review discusses in depth the involvement of O-GlcNAcylation in the precise regulation of skeletal muscle metabolism, such as glucose homeostasis, insulin sensitivity, tricarboxylic acid cycle and mitochondrial biogenesis. The complex interaction and precise modulation of O-GlcNAcylation in these nutritional pathways of skeletal muscle also provide emerging mechanical information on how nutrients affect health, exercise and disease. Meanwhile, we explored the potential role of O-GlcNAcylation in skeletal muscle pathology and focused on its benefits in maintaining proteostasis under atrophy. In general, these understandings of O-GlcNAcylation are conducive to providing new insights into skeletal muscle (patho) physiology.